1. Field of the Invention
The present invention relates to an eye direction detecting device that is provided, for example, in a view finder of a camera for detecting a specific point in the view finder at which a photographer's eye gazes.
2. Description of Related Art
An eye direction detecting device (referred to hereinafter as an eye detector) is known, as disclosed, for example in U.S. Pat. No. 5,036,347. In a known eye detector used in a single lens reflex camera, a bundle of rays emitted from a light source, such as a light emitting diode (LED), is made incident upon a photographer's eye through an eyepiece of the view finder. Light reflected by the photographer's eye is converged and received by a light receiving element, such as a CCD sensor, whose output is electrically processed to detect the direction of sight.
In such a known eye detector, outgoing light that is incident upon the photographer's eye, and return light reflected therefrom are transmitted through the eyepiece along the same optical path. Accordingly, it is necessary to provide a beam splitter between the light source and the eyepiece to split the return light path from the incident light path. The beam splitter is usually made of a half mirror.
However, when light is twice transmitted through (or reflected by) the half mirror, the quantity of light which can be received by, the light receiving element will, theoretically, be one fourth the quantity of light emitted by the light source. This is assuming that the quantity of light has not been diminished by optical elements other than the beam splitter.
It is therefore necessary to increase the output of the light source to obtain a sufficient quantity of light for detecting a viewer's line of sight.